4-line CCD sensor and image input apparatus using the same

ABSTRACT

A 4-line CCD sensor according to one embodiment of the present invention has a monochromic reading line sensor section and a color reading line sensor section. This 4-line CCD sensor is characterized in that amplification factors for amplifiers  1  to  4  are set so that the amplitude of an output signal from the monochromic reading line sensor section is the same as that of each output signal from the color reading line sensor section. This 4-line CCD sensor is characterized in that the amplification factors for the amplifiers  1  to  4  are set so that the amplitude of each output signal from the color reading line sensor section is smaller than that of an output signal from the monochromic reading line sensor section.

The present application is a continuation of U.S. application Ser. No.10/377,818, filed Mar. 4, 2003, the entire contents of which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

Today, 4-line CCD sensors are commercially available and are commonlyused. The 4-line CCD sensor comprise a monochromic reading sensor inwhich no color filters are arranged on a light receiving surface of aphotodiode array in order to read monochromic originals, and a colorreading 3-line sensor in which color filters for red, green, and blue(hereinafter referred to as R, G, and B), i.e. the three primary colors,are arranged on the light receiving surfaces of the respectivephotodiode arrays composed of the same material, in order to read acolor original, the monochromic reading line sensor and the colorreading 3-line sensor being constituted by the same chip.

The structure of the CCD line sensor is disclosed in Jpn. Pat. Appln.KOKAI Publication No. 2-76361. Driving of the CCD sensor is disclosed inJpn. Pat. Appln. KOKAI Publication Nos. 11-220569 and 2000-69254.

In this case, sensitivity, an electric characteristic of the CCD linesensor is defined by output power [V/lx. sec] with respect to thequantity of incident light per unit time. Thus, with a 4-line CCD sensorcomposed of a plurality of CCD sensors, even if the CCD sensors, i.e.the photodiode arrays are irradiated with uniform light energy, i.e. thesame quantity of light over the same period, the amplitudes of outputsignals from the CCD sensors vary according to the transmittalwavelength through the color filters arranged on the light receivingsurfaces.

In view of these points, an image input apparatus according to the priorart matches the amplitudes of output signals from the CCD sensors to oneanother by adjusting the spectral characteristic of a light sourceaccording to the sensitivities of a plurality of CCD sensors. Further,if the output signals from the CCD sensors have different amplitudes,the amplitudes of the output signals are matched to one another byadjusting, according to the amplitudes of the output signals, theamplification factor of an amplifier succeeding the CCC sensors, e.g. again amplifier composed of an operational amplifier or the like.

On the other hand, with a scanner section as an image input apparatusused for recent color readable digital copiers and digital compositemachines, the succeeding circuit carries out adjustment even with theuse of a light source having its spectral characteristics limited tosome degree.

BRIEF SUMMARY OF THE INVENTION

The present invention is provided in view of the above problems. It isan object of the present invention to provide a 4-line CCD sensor thatrealizes appropriate gradation merely by easy adjustment or without anyadjustment using a simple circuit configuration, as well as an imageinput apparatus that can use a simple and inexpensive circuitconfiguration to realize application-based image inputs, e.g. high-speedcolor reading for low gradation and low-speed color reading for highgradation.

To accomplish the above object, the 4-line CCD sensor or image inputapparatus according to an embodiment of the present invention has amonochromic reading line sensor section composed of a monochromicphotodiode array which receives incident light from a light source whichemits a large quantity of white light, to carry out photoelectricconversion according to the quantity of incident light, a monochromicshift gate which transfers charges from the monochromic photodiodearray, a monochromic analog shift register which receives the chargesfrom the monochromic shift gate to transfer an electric signal, and amonochromic amplifier which has an amplification factor set according toa spectral characteristic of the light source and amplifies an electricsignal from the monochromic analog shift register with thisamplification factor to output the amplified electric signal to anexterior, and a color reading line sensor section composed of colorphotodiode arrays each of which receives incident light from the lightsource to carry out photoelectric conversion according to the quantityof the incident light, color shift gates each of which transfers chargesfrom the color photodiode array, a color analog shift register whichreceives the charges from the color shift gate to transfer an electricsignal, and color amplifiers each of which has an amplification factorset according to the spectral characteristic of the light source andamplifies an electric signal from the color analog shift register withthis amplification factor to output the amplified electric signal to theexterior.

Additional objects and advantages of the invention will be set forth inthe description which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. The objectsand advantages of the invention may be realized and obtained by means ofthe instrumentalities and combinations particularly pointed outhereinafter.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate presently preferred embodiments ofthe invention, and together with the general description given above andthe detailed description of the embodiments given below, serve toexplain the principles of the invention.

FIG. 1 is a conceptual diagram showing an example of configuration of a4-line CCD sensor on which a first and second embodiments of the presentinvention are based;

FIG. 2A is a graph showing the spectral sensitivity characteristic of amonochromic reading line sensor section in the 4-line CCD sensor, andFIG. 2B is a graph showing the spectral sensitivity characteristic of acolor reading line sensor section in the 4-line CCD sensor;

FIG. 3 is a graph showing the spectral distribution characteristic of awhite xenon light source;

FIGS. 4A and 4B are timing charts showing driving timings for each lineof the 4-line CCD sensor on which a first and second embodiments of thepresent invention are based;

FIG. 5 is a timing chart showing driving timings for each pixel of the4-line CCD sensor on which a first and second embodiments of the presentinvention are based;

FIG. 6 is a conceptual drawing showing an example of configuration of animage input apparatus using the 4-line CCD sensor according to thesecond embodiment of the present invention; and

FIG. 7 is a block diagram of an analog signal processing circuitemployed in the image input apparatus according to the second embodimentof the present invention to process CCD output signals.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will be described with reference tothe drawings.

FIG. 1 schematically shows an example of configuration of a 4-line CCDsensor on which a first and second embodiments of the present inventionare based. This 4-line CCD sensor will be described in detail.

As shown in FIG. 1, this 4-line CCD sensor is composed of a monochromicreading line sensor section and a color image reading 3-line sensorsection (specifically, the color image reading 3-line sensor section iscomposed of a blue reading line sensor section, a green reading linesensor section, and a red reading line sensor section).

First, the monochromic reading line sensor section is composed of amonochromic photodiode array 5, a monochromic shift gate 6, amonochromic analog shift register 7, and an amplifier 1. No colorshifters are arranged on a light receiving surface of the monochromicphotodiode array 5. With this configuration, upon receiving amonochromic shift pulse, the monochromic shift gate 6 transfers chargesphotoelectrically converted by the monochromic photodiode array 5according to the quantity of incident light, to the succeedingmonochromic analog shift register 7. Upon receiving transfer clocks 1and 2, the monochromic analog shift register 7 sequentially transferscharges photoelectrically converted by the monochromic photodiode array5 and obtained via the monochromic shift gate 6. The amplifier 1 outputsan output signal from the monochromic analog shift register 7 to anexterior.

Further, the blue reading line sensor section is composed of a bluephotodiode array 8, a blue shift gate 9, a blue analog shift register10, and an amplifier 2. A blue color filter is arranged on a lightreceiving surface of the blue photodiode array 8. With thisconfiguration, upon receiving a blue shift pulse, the blue shift gate 9transfers charges photoelectrically converted by the blue photodiodearray 8 according to the quantity of incident light, to the succeedingblue analog shift register 10. Upon receiving transfer clocks 1 and 2,the blue analog shift register 10 sequentially transfers the chargesphotoelectrically converted by the blue photodiode array 8 and obtainedvia the blue shift gate 9. The amplifier 2 outputs an output signal fromthe blue analog shift register 10 to the exterior.

The green reading line sensor section is composed of a green photodiodearray 11, a green shift gate 12, a green analog shift register 13, andan amplifier 3. A green color filter is arranged on a light receivingsurface of the green photodiode array 11. With this configuration, uponreceiving a green shift pulse, the green shift gate 12 transfers chargesphotoelectrically converted by the green photodiode array 11 accordingto the quantity of incident light, to the succeeding green analog shiftregister 13. Upon receiving transfer clocks 1 and 2, the green analogshift register 13 sequentially transfers the charges photoelectricallyconverted by the green photodiode array 11 and obtained via the greenshift gate 12. The amplifier 3 outputs an output signal from the greenanalog shift register 13 to the exterior.

Furthermore, the red reading line sensor section is composed of a redphotodiode array 14, a red shift gate 15, a red analog shift register16, and an amplifier 4. A red color filter is arranged on a lightreceiving surface of the red photodiode array 14. With thisconfiguration, upon receiving a red shift pulse, the red shift gate 15transfers charges photoelectrically converted by the red photodiodearray 14 according to the quantity of incident light, to the succeedingred analog shift register 16. Upon receiving transfer clocks 1 and 2,the red analog shift register 16 sequentially transfers the chargesphotoelectrically converted by the red photodiode array 14 and obtainedvia the red shift gate 15. The amplifier 4 outputs an output signal fromthe red analog shift register 16 to the exterior.

FIG. 2A shows the spectral sensitivity characteristic of the monochromicphotodiode array 5, which has no color filters arranged on its lightreceiving surface. FIG. 2B shows the spectral sensitivity characteristicof the color reading 3-line sensor section, which has the red, green,and blue color filters arranged on the light receiving surfaces. Eachline sensor of the 4-line CCD sensor already shown in FIG. 1 has thespectral sensitivity characteristic shown in FIG. 2B. The spectralsensitivity characteristic is determined by a photoconductive materialused as well as production conditions. In these figures, the axis ofabscissa indicates an incidence wavelength λ (nm). The axis of ordinateindicates a signal current resulting from light energy incident on ascanning surface, in terms of relative sensitivity (%). As shown inFIGS. 2A and 2B, an incident light wavelength related to the peak of therelative sensitivity varies among BK, R, G, and B. In the figures, themaximum value of red is defined to have a relative value (relativesensitivity) of 1, with the other colors relatively defined.

FIG. 3 shows the spectral characteristic of a white xenon light sourceas an example of a light source.

In the example of FIG. 3, the axis of abscissa indicates wavelength(nm), while the axis of ordinate indicates a relative value (%). Today,a xenon light source is commonly used because it is characterized byemitting a continuous spectrum approximate to daylight and providinghigh luminance. A white fluorescent lamp provides a large quantity oflight, and a halogen light source generates less heat.

FIGS. 4A and 4B show an example of driving timings for each line of the4-line CCD sensor. FIG. 5 shows an example of driving timings for eachpixel of the 4-line CCD sensor. Specific operations will be describedbelow. Specific operations of the image input apparatus will bedescribed later.

First, with reference to FIGS. 4A and 4B, description will be given ofexample of driving timings for each line of the 4-line CCD sensor.

Light emitted by a white xenon light source having such a spectralcharacteristic as shown in FIG. 3 is reflected by a surface of anoriginal and then impinges against the light receiving surfaces of thephotodiode arrays 5, 8, 11, and 14 of the 4-line CCD sensor.

The monochromic shift pulse is a control signal for the monochromicshift gate. When the monochromic shift pulse is at an “H” level, chargesphotoelectrically converted by the monochromic photodiode array 5 aretransferred to the monochromic analog shift register 7 via themonochromic shift gate 6. Then, the charges transferred to themonochromic analog shift register 7 are sequentially transferred in anoutput direction according to transfer clocks 1 and 2. The charges arethen output to the exterior via the amplifier 1 in an output stage.

With the color reading 3-line CCD sensor, when the blue shift pulse, thegreen shift pulse, and the red shift pulse are at the “H” level, chargesare transferred to the blue analog shift register 10, the green analogshift register 13, and the red analog shift register 16, respectively,via the blue shift gate 9, the green shift gate 12, and the red shiftgate 15, respectively. Then, the charges are sequentially transferred inthe output direction according to the transfer clocks 1 and 2. Thecharges are then output from the blue analog shift register 10 via theamplifier 2 in the final output stage, from the green analog shiftregister 13 via the amplifier 3 in the final output stage, and from thered analog shift register 16 via the amplifier 4 in the final outputstage, respectively.

In this example, the phases of the transfer clocks 1 and 2 are displacedfrom each other by 180° and each have a duty ratio (the ratio of the “H”level and a “L” level) set at 50%.

Now, with reference to FIG. 5, a detailed description will be given ofan example of driving timings for each pixel of the 4-line CCD sensor.

As shown in FIG. 5, in this example, a reset pulse and a clamp pulse,shown in the figure, are inputted with the same period as that of thetransfer clocks 1 and 2.

Charges outputted by the analog shift registers 7, 10, 13, and 16 aretransferred to a floating capacitor section in the final stage (notshown).

The floating capacitor section normally has a certain fixed potential.When charges are outputted by the analog shift register 7, 10, 13, or16, the potential at the floating capacitor varies. Furthermore, in thisexample, once the charges have been completely transferred, the resetpulse is inputted to perform an operation of returning the potential atthe floating capacitor to a reference potential. This is because if thisoperation is not performed, the charges outputted by the analog shiftregisters 7, 10, 13, and 16 are gradually accumulated, which hinders thesignal from being cut up into pixels.

A signal is essentially outputted by the CCD sensor when the transferclocks 1 and 2 and the reset pulse are inputted to the registers.

This will be described using the output waveform in the lowest stage.

The reference potential at the floating capacitor section appears like aDC output voltage (VOS), i.e. an offset component from the referencepotential (GND=0 V), as viewed from an output signal. The reset pulsecauses a reset noise to be superimposed on the DC output voltage (VOS).The superimposed section is followed by a stable section called a “fieldthrough”. Subsequently, charges are outputted by the analog shiftregister at a rising edge of the transfer clock 2. As shown in thefigure, a signal is outputted downward from the DC output voltage. Inthis case, a phenomenon occurs in which the potential at the floatingcapacitor section is unstably fluctuated by operations of a reset gate(not shown) controlled by a reset pulse. It is known that thisfluctuation is also superimposed on an effective signal part. To preventthis phenomenon, the reset pulse is inputted after the reset pulse tostabilize the potential at the field through section. This serves toreduce the fluctuation of the effective signal part. The 4-line CCDsensor has different effective signal amplitudes for the respectivechannels in order to perform the above operation.

FIRST EMBODIMENT

On the basis of the above preconditions, a detailed description will begiven of a 4-line CCD sensor according to a first embodiment of thepresent invention. The 4-line CCD sensor according to the firstembodiment is characterized in that the light source used is limited toa white xenon light source and in that the amplification factor of anoutput amplifier section in each output stage is determined.

The general configuration of the 4-line CCD sensor on which the firstembodiment of the present invention is based is similar to that shown inFIG. 2. Its description is thus omitted.

In the 4-line CCD sensor according to the first embodiment,predetermined amplification factors (GAIN: A, B, C, and D) are set forthe amplifiers 1, 2, 3, and 4, provided in the output stages of theanalog shift register sections 7, 10, 13, and 16.

The blue, green, and red color filters arranged on the light receivingsurfaces of the photodiode array sections 8, 11, and 14 each have such arelative transmittance as shown in FIG. 2B. As is apparent from thisfigure, the 4-line CCD sensor has the photodiode arrays 8, 11, and 14with the color filters arranged on their light receiving surfaces andthe photodiode array 5 with no color filters arranged on its lightreceiving surface. Furthermore, as shown in FIG. 3, the spectralcharacteristic of the white xenon light source does not exhibit auniform wavelength distribution. Accordingly, the amounts of chargesoutputted by the analog shift registers 7, 10, 13, and 16 are not equal.

That is, when the amount of charges outputted by the monochromic analogshift register 7 is assumed to be 1.0, the amounts of charges outputtedby the registers are as shown below.

-   Monochromic analog shift register output: 1.0-   Blue analog shift register output: 0.5-   Green analog shift register output: 0.6-   Red analog shift register output: 0.8

Then, when a white xenon light source is used to read an original, thesevalues must be equal. Consequently, the amplification factors of theamplifiers 1 to 4, shown in FIG. 1, may be set as shown below.

-   GAIN A: multiplied by 1.00 (1.0×1.00)-   GAIN B: multiplied by 2.00 (0.5×2.00)-   GAIN C: multiplied by 1.67 (0.6×1.67)-   GAIN D: multiplied by 1.25 (0.8×1.25)

When these amplification factors are set for the amplifiers 1 to 4,respectively, if a white xenon light source is used, the effectiveoutput amplitudes of output signals equal one another. Therefore,according to the first embodiment of the present embodiment provides a4-line CCD sensor characterized in that the internal amplificationfactors are matched to one another on the basis of the white xenon lightsource.

Now, description will be given of an improved example of the 4-line CCDsensor according to the first embodiment of the present invention. Inthe first embodiment, all output signal amplitudes are intentionallymatched to one another. However, in this improved example, attention ispaid to advantages of an intentional variation in output signalamplitude.

Now, the amount of charges outputted by the monochromic analog shiftregister is assumed to be 1.0 . Then the amounts of charges outputted bythe registers are as shown below.

-   Output from the monochromic analog shift register: 1.0-   Output from the blue analog shift register: 0.5-   Output from the green analog shift register: 0.6-   Output from the red analog shift register: 0.8

In this improved example, when a white xenon light source is used toread a white original, the balance of these values is intentionallychanged. That is, the amplification factors of the amplifiers 1 to 4 areas shown below.

-   GAIN A: multiplied by 1.00 (1.0×1.00)=X-   GAIN B: multiplied by 1.00 (0.5×1.00)=X×½-   GAIN C: multiplied by 0.83 (0.6×1.83)=X×½-   GAIN D: multiplied by 0.62 (0.8×0.62)=X×½

These settings make the amplitude value of color signals half of theamplitude value of a monochromic output signal. That is, according tothis improved example, the amount of charges stored in each photodiodearray can be limited by setting a light storage time tINT (see FIG. 4A)required to read a colored original to be double a light storage timetINT required to read a monochromic original. Further, the output signalamplitudes can be matched to one another by setting the amplificationfactors of the amplifiers in the final stages. Further, the succeedingcircuit can be easily configured by integrally multiplying the speedratio.

SECOND EMBODIMENT

FIG. 6 shows a configuration of an image input apparatus employing a4-line CCD sensor according to a second embodiment of the presentinvention. In the present embodiment, a 4-line CCD sensor 54 is, forexample, the one shown in FIG. 1. Furthermore, in the presentembodiment, the spectral characteristic of a light source must bespecified. Accordingly, a white xenon light source having the spectralcharacteristic in FIG. 3 is employed as a light source 52. However, ofcourse, the light source 52 may be a fluorescent lamp, a halogen lamp,or the like.

As shown in FIG. 6, a first mirror 64, a second mirror 56, a thirdmirror 57, and a condensing lens 59 are disposed in an optical path forlight reflected by an original O at its reading position P, the lightbeing emitted by the light source 52, covered with a reflector 53. The4-line CCD sensor 54 is disposed on an optical axis of the condensinglens 59. The 4-line CCD sensor 54 is disposed on a CCD substrate 60. TheCCD substrate 60 is electrically connected to a CCD control substrate61. The light source 52, the reflector 53, and the first mirror 64 aredisposed in a second carriage 58.

Copy glass plate 63 on which an original is placed is located over theimage input apparatus 51. An original fixing cover 62 is disposed overthe copy glass plate 63. The 4-line CCD sensor 10 and a sensor drivingcircuit (not shown) are mounted on the CCD substrate 60. The CCD controlsubstrate 61 is provided with a control circuit composed of a CPU or thelike to control the 4-line CCD sensor 54 and an image processing circuit(not shown) that processes an output signal from the 4-line CCD sensor54.

With such a configuration, the original O is placed on the copy glassplate 63. The original fixing cover 62 is then used to contact theoriginal O with the copy glass plate 63 for fixation.

Then, the image input apparatus 51, for example, turns on the lightsource 52 to irradiate the original O with light. Light reflected by theoriginal O at the reading point P passes through the copy glass plate 63and is then reflected by the first mirror 64, the second mirror 56, andthe third mirror 57 in this order. The reflected light is formed into animage on the light receiving surface of the 4-line CCD sensor 54 via thecondensing lens 59. Then, the 4-line CCD sensor 54 converts the lightreflected by the original O and then formed into the image on the lightreceiving surface of the 4-line CCD sensor 54, from optical energy intoan electric signal. Furthermore, the signal processing circuit section(not shown) on the succeeding CCD control circuit 61 executes variousprocesses.

A first carriage 55 and a second carriage 58 move at speeds 2V and V,respectively, in the direction shown in the figure. Accordingly, thereading position P on the original also moves. Thus, an optical pathlength, i.e. the distance from the reading position P to the 4-line CCDsensor 54, is kept fixed.

FIG. 7 shows the detailed configuration of the CCD control circuit 12.

An analog signal from the 4-line CCD sensor 54 is inputted to the CCDcontrol circuit 61. This signal contains a DC output voltage (VOS). ThisDC component is not required for the succeeding process. Thus, acoupling capacitor 101 is inserted between the 4-line CCD sensor 54 andthe succeeding circuit to remove the DC output voltage, i.e. the DCcomponent. The signal free from the DC component is provided with anoffset suitable for the succeeding process.

Subsequently, an effective signal part is stabilized by a sample andhold circuit 103. The amplitude of the effective signal part is thenadjusted by a gain amplifier circuit 104 composed of an operationalamplifier so as to conform to the input range of the succeeding A/Dconverter 105 that converts an analog signal into a digital signal.Then, the A/D converter 105 converts the effective signal part into adigital signal. The upper limit of input range of the A/D converter 105is set using a reference voltage VERF-H, while its lower limit is setusing a reference voltage VREF-L. Thus, the signal processed by the gainamplifier circuit 104 has a signal amplitude between the referencevoltage VREF-L and the reference voltage VREF-H. Subsequently, thesignal is converted so as to have a required resolution, and theconverted signal is then subjected to various processes by thesucceeding digital signal processing system (not shown). In the examplein FIG. 7, the resolution is 10 bits, but of course the presentinvention is not limited to this aspect.

Thus, the A/D converter 105 provides a digital signal ranging from thelower limit VREF-L of the reference voltage and the result of conversion“000H” of this potential to the upper limit VREF-H of the referencevoltage and the result of conversion “3FFH” of this voltage. Theprocessing system from the coupling capacitor 102 to the A/D converter105 is required for each color. There are thus four processing systemsfor monochromic signal processing, blue signal processing, green signalprocessing, and red signal processing.

In the second embodiment, all sensitivities of the 4-line CCD sensor 54,shown in FIG. 6, have the same amplitude if the white xenon light source52 is used to read a white original. Thus, the amplification factors ofthe gain amplifier circuits 104 in the four systems can be taken ashaving the same value. This serves to simplify the circuit and reduceits costs.

Further, it is assumed that the sensitivities of the 4-line CCD sensor54, shown in FIG. 6, are set so that if the white xenon light source 52is used to read a white original, the signal amplitude of each color,i.e. blue, green, or red is half that of black and white. Then, theoutput amplitudes are made equal by reading monochromic originals athigh speed and doubling the light storage time (tINT) for reading ofcolored originals compared to reading of monochromic originals. In thiscase, the periods of the transfer clocks 1 and 2 and reset and clamppulses, which control operations for each pixel, are doubled, i.e. theirfrequencies are reduced to half compared to monochromic originals.Consequently, analog signals with a good S/N can be obtained. Thus, inthis case, when a colored original is read, a signal with a good S/N andgradation can be obtained.

In the above description, the ratio of an output from the amplifier 20,i.e. a monochromic output signal, to an output from the amplifier 21,i.e. a blue output signal, to an output from the amplifier 22, i.e. agreen output signal, to an output from the amplifier 23, i.e. a redoutput signal is 2:1:1:1. Similar advantages are obtained by settingthis ratio at the integral power of 2 such as in 4:1:1:1 (n:1:1:1, n=2,4, 8, . . . ).

Further, the blue photodiode array 27, green photodiode array 30, andred photodiode array 33, which are used to read a colored image, arephysically spaced from one another. That is, strictly speaking, theposition at which the original O is read varies. Accordingly, thesucceeding digital signal processing section must execute such a processthat image signals for the respective colors correspond to the sameposition. This process can be easily organized by setting the signalamplitude of an output from the amplifier 20 to be larger than thesignal amplitudes of outputs from the amplifiers 21 to 23 by a factor ofintegral power of 2 and setting the ratio of the monochromic readingspeed to the color reading speed to be the integral power of 2.

Another example will be given in which the sensitivities of the 4-lineCCD sensor 54, shown in FIG. 6, are set so that if the white xenon lightsource 52 is used to read a white original (original O) using a lightstorage time with the same period, then the signal amplitude of eachcolor, i.e. blue, green, or red is half that of black and white. In thisexample, the amplitude of each of the blue, green, and red outputs ishalf that of the monochromic output. In this case, the process can beadjusted by setting the amplification factor of the gain amplifiercircuits 104 to be double that of the gain amplifier 104 for themonochromic system. However, a fixed amount of noise component iscontained in each output signal from the CCD sensor, so that the amountof charges decreases after photoelectric conversion. Consequently, theS/N decreases to provide image signals with a large amount of noise.However, if a colored image is inputted for filing, which does notrequire gradation, then it can be read at a reading speed equivalent tothe one at which monochromic images are read.

Further, for photographic images or the like, which require gradation, acolored image with a good S/N can be obtained by doubling the lightstorage time (tINT) and reducing the reading speed to half compared tomonochromic images when a colored original is read.

As described above, the above embodiments of the present inventionprovide a 4-line CCD sensor with its amplification factors set so thatthe amplitudes of output signals from the line sensors are matched toone another according to the spectral characteristic of the light sourceused, as well as an image input apparatus using this 4-line CCD sensor.This serves to realize proper gradation by easy adjustment or withoutany adjustment using a simple circuit configuration.

The above embodiments of the present invention provide a 4-line CCDsensor with its amplification factors set so that the amplitude of anoutput signal from the monochromic line sensor is larger than that ofoutput signals from the color reading line sensors by a factor ofintegral power of 2, as well as an image input apparatus using thisimage input apparatus. This serves to provide a system with propergradation accomplished by easy adjustment or without any adjustmentusing a simple circuit configuration.

Furthermore, the above embodiments of the present invention provide a4-line CCD sensor with its amplification factors set so that theamplitude of an output signal from the monochromic line sensor is largerthan that of output signals from the color reading line sensors by afactor of integral power of 2, as well as an image input apparatus usingthis image input apparatus. This enables an application-based system tobe constructed using a simple circuit configuration, the system beingsuch that high-speed color reading is executed for low gradation,whereas low-speed color reading is executed for high gradation.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. An image input apparatus comprising: a light source having a whitespectral characteristic; a 4-line CCD sensor having a monochromicreading line sensor section composed of a monochromic photodiode array,a monochromic shift gate, a monochromic analog shift register, and amonochromic amplifier which has an amplification factor set according tothe spectral characteristic of the light source and which amplifies anelectric signal from the monochromic analog shift register with thisamplification factor to output the amplified electric signal to anexterior, a color reading line sensor section composed of colorphotodiode arrays, color shift gates, color analog shift registers, andcolor amplifiers each of which has an amplification factor set accordingto the spectral characteristic of the light source and which amplifiesan electric signal from the color analog shift register with thisamplification factor to output the amplified electric signal to theexterior; and a control circuit, which controls the 4-line CCD sensor.2. The image input apparatus according to claim 1, wherein the controlcircuit which sets the amplification factor so that the amplitude of anoutput signal from the monochromic reading line sensor section is thesame as that of each output signal from the color reading line sensorsection.
 3. The image input apparatus according to claim 1, wherein thecontrol circuit which sets the amplification factor so that theamplitude of the output signal from the monochromic reading line sensorsection is different from that of the output signal from the colorreading line sensor section.
 4. The image input apparatus according toclaim 1, wherein the control circuit which sets the amplification factorso that the ratio of amplitude of the output signal from the monochromicreading line sensor section to the amplitude of the output signal fromthe color reading line sensor section is an integral power of 2, andlimits a speed range for reading to facilitate alignment of signalsoutputted by the color reading line sensor section.
 5. The image inputapparatus according to claim 1, wherein the control circuit which makesa monochromic reading speed lower than a color reading speed to readdata representing color images of enhanced gradation.